The invention relates to an arrangement for controlling fuel flow to an internal-combustion engine, especially a diesel internal-combustion engine, and comprising a fuel-injection pump, a mechanically driven pre-supply pump for supplying fuel from a fuel tank to the suction space of the fuel injection pump, an electro-magnetic control valve located downstream of the pre-supply pump and upstream of the suction space and movable between a supply position in which fuel flows from the pre-supply pump into the suction space, and a disconnected position, and an additional suction supply pump for communicating the suction space with the fuel tank in the disconnected position of the control valve.
German Offenlegungsschrift 3,304,355 discloses a control arrangement of the particular generic type, in which, in an alternative solution according to the embodiment FIG. 2, an electrically driven supply pump with a pole-changing electric motor and reversible feed device is used to stop the internal-combustion engine. Upon cutoff of the internal-combustion engine, the suction space of the fuel-injection pump is connected to the suction side of the supply pump, and the delivery side of the supply pump is connected to the fuel tank.
In the event of a cutoff, fuel is thereby extracted abruptly from the suction space of the fuel-injection pump, so that the fuel-injection pump can no longer deliver fuel, and the associated internal-combustion engine stops.
It has been shown that, in this known control arrangement, the suction effect of the supply pump of bipolar design in the flow part, that is to say working in both directions of rotation and therefore fundamentally not optionally adjustable, is not always sufficient to generate a high enough vacuum in the suction space of the injection pump as quickly and as abruptly as possible. This does not ensure a satisfactory cutoff of the internal-combustion engine, and consequently the danger of engine damage as a result of overspeeding an excess quantity of fuel and of accidents, is not prevented sufficiently reliably because "gas cutoff" is not possible.
A further disadvantage of this solution is that peripheral suction and delivery lines of the supply pump working in two supply directions have to be uncoupled hydraulically, this necessitating additional components, for example additional non-return valves. This involves a high outlay in terms of constructional space and cost and constitutes an undesirable safety risk in that. If one of these additional components functions inadequately or even fails, the entire system can break down. Moreover, the total outlay for the use of reversible electric fuel pumps on diesel engines is considerable because of the additional current supply and the control circuit required.
In a further alternative solution (according to the embodiment of FIG. 1 of German Offenlegungsschrift 3,304,355), in addition to a supply pump serving only for delivering to the suction space of the fuel-injection pump, there is provided a second electrically driven supply pump which comes into operation only in the event of the cutoff of the internal-combustion engine. It is activated and operated electrically via an electronic control unit which interacts with an electrohydraulic injection-pump controller. This system involves a high outlay and is cost-intensive and with the degree of complexity and mutual dependence increases the risk of failure.